1. Field of the Invention
This invention relates to television standards converters.
2. Description of the Prior Art
Television standards converters are well known devices used to convert video signals from one television standard to another, for example, from a 625 lines per frame, 50 fields per second (625/50) standard to a 525 lines per frame, 60 fields per second (525/60) standard. Video standards conversion cannot be achieved satisfactorily merely by using simple linear interpolation techniques, because of the temporal and vertical alias which is present in a video signal. Thus, simple linear interpolation produces unwanted artefacts in the resulting picture, in particular, the pictures are blurred vertically and judder temporally.
To reduce these problems it has been proposed that video standards converters should use adaptive techniques to switch the parameters of a linear interpolator in dependence on the degree of movement in the picture represented by the incoming video signal.
`Methods of Gradient Vector Compensated Image Processing` by J H Wilkinson and G A Walker, Third Image Processing Conference, 1989, outlines investigations into techniques for creating accurate gradient vectors used as pointers for intra-field interpolation of 2:1 interlaced scanning systems.
Attention is also drawn to Sony Corporation's European patent specification EP-A1-0 393 906 which discloses subject matter generally similar to that of the above-mentioned paper. The present invention is concerned with the further problem of creating accurate motion vectors which can be used as pointers for inter-field interpolation, thereby enabling a television standards converter to be developed.